mConnect and BubbleUpnP do not discover MinimServer

[Pepsican]

Hi

My issue is as follows:
Neither BubbleUPnP, nor mConnect will discover MinimServer, or they will discover it very slowly. It can easily take up to 15 minutes to discover MinimServer (by then I will give up and use something else to play music). And sometimes it will then disappear again. Bubble seems to be a little faster than mConnect to discover MinimServer, if it manages to find it. MinimWatch is also slow in finding MinimServer, but is much more rapidd than the cvontrol points. It will find it in under 2 minutes typically.

My network
- Router/Modem from ISP (Arris TG2492S). This device only acts as a Gateway/Router and it does some port forwarding for my game console.
- TP-Link SG2008P smart PoE switch. It does DHCP and the advanced L2/L3 switching (QoS, VLAN, etc), for as far as there is any.
- 2 TP-Link APs for WiFi
- Synology DS214+ on DSM 7.1 with MinimServer 248 installed
- Control points: Android12 phone with BubbleUPnP (licensed) and Apple iPad with iOS 17.4 and mConnect Lite
- Windows 10 on all PCs and Laptops on the latest version.

What I have done so far
- Added a rule to the Synology firewall to leave any MinimServer traffic alone (as found here on the forum)
- Checked everywhere (modem, switch, NAS) that IGMP Snooping is off (it is)
- UPnP is turned off for security reasons
- Defined the subnet in ohnet.subnet
- No Firewalls are blocking MinimServer traffic

Question: what am I missing to make these two control points find minimserver faster?